With traditional extrusion a billet of material is pushed and/or drawn through a die to create a rod, rail, pipe, etc. Various applications leverage this capability. For instance, extrusion can be used with food processing applications to create pasta, cereal, snacks, etc., pipe pastry filling (e.g., meringue), pattern cookie dough on a cookie pan, generate pastry flowers and borders on cakes, etc. In another application, extrusion can be used with consumer goods, for example, to merge different colored toothpastes together on a toothbrush.
Conventional extrusion techniques are limited, for example, in that they cannot render relatively high aspect-ratio (e.g., 2:1 or greater) fine featured (e.g., less than 50 micron) or porous structures. Thus, extrusion typically is not used for creating conducting contacts and/or channels for electrochemical (e.g., fuel), solar, and/or other types of cells, which leverage high aspect-ratio fine featured porous structures to increase efficiency and electrical power generation.
By way of example, with fuel cells, high aspect-ratio fine featured porous electrolyte structures provide a long reaction zone that increases utilization of the expensive catalyst needed for the electrode. In addition, fuel cells can be complex structures since they perform multiple functions including: conducting protons from the membrane to the reaction site; diffusing oxygen to the reaction site with a low partial pressure drop; conducting electrons from the porous electrode to the reaction site; carrying heat away from the reaction site; and withstanding a compressive mechanical load in a range of about 100 to 200 PSI. Conventional extrusion techniques cannot meet these demands at a cost demanded by the fuel cell industry. In order to increase efficiency, fuel cell manufacturers use more catalyst than desired to increase the number of reaction sites and make agglomerates of carbon catalyzed with Platinum (Pt) in a matrix of porous, or polytetrafluoroethylene (PTFE). With solar cells, high aspect-ratio fine featured grid lines reduce the amount of shading, which allows more photons to be captured, resulting in an increased electrical power generation. Conventional extrusion techniques are not able to produce such gridlines at a cost demanded by the solar cell industry.
There are many other practical devices that benefit from rapid and economical means for generating high aspect ratio lines and features. FIG. 12 shows, by way of example, a plasma display panel as an example of a device that incorporates barrier ribs that define the sub-pixels within the display. The barrier rib is an electrically insulating structure, and is preferably a high aspect ratio structure, as this improves the dot per inch resolution and fill factor of the display.
What is needed is a system and method for efficiently producing closely spaced, high aspect-ratio gridlines that can be used, for example, in the production of high quality photovoltaic cells and plasma display panels.